1. Field of the Invention
The invention relates to an image forming apparatus which is suitably usable for a copying machine, a printer, a plotter, a facsimile or similar printing apparatus.
2. Description of Related Art
A conventionally known image forming apparatus is disclosed in U.S. Pat. No. 3,689,935. The apparatus uses an electrode having plural opening portions (hereinafter referred to as "apertures") and a voltage is applied to the electrode in accordance with image data to control passage of toner particles through the apertures, whereby an image is formed on a supporter (image receiving medium) with the passed toner particles.
The image forming apparatus includes an aperture electrode unit comprising an insulating flat plate, a reference electrode formed continuously on one surface of the flat plate, plural control electrodes which are formed on the other surface of the flat plate and are electrically insulated from one another and at least one row of apertures, an aperture formed in correspondence with each control electrode so as to penetrate through the flat plate, the reference electrode and the corresponding control electrode; means for selectively applying a voltage across the reference electrode and the control electrodes; means for supplying charged toner particles so that the flow of the toner particles passed through the apertures is modulated in accordance with the applied voltage; and means for moving a supporter and the aperture electrode unit relative to one another to position the supporter in a particle flow passage.
However, in this apparatus, recording quality is liable to be degraded due to clogging of the apertures with toner particles and the recording speed cannot be set to a high value.
European Unexamined Patent Publication No. 587,366 discloses an image recording apparatus which is capable of improving the recording characteristic by disposing a carry member for holding toner and an aperture electrode unit so that these members are brought into contact with each other. According to this apparatus, the toner is supplied to the aperture electrode unit while brought into contact with the peripheral portions of apertures of the aperture electrode unit so that there is no toner deposition which will cause the clogging of the apertures with the toner. Thus, the apertures are prevented from being clogged.
However, in the conventional image forming apparatus as described above, a high driving voltage is required to force the toner to be separated from a carry member and to fly toward a supporter (image receptor) side because the toner is supplied onto the carry member while adhering to the carry member due to image force, van der Waals force, etc. The result is the total manufacturing cost of the apparatus containing a driving element is high.